Morphological response to Lake Bardawil adaptations

Abstract

Bardawil Lagoon is a tidal lagoon situated at the northern coast of the Sinai Peninsula in Egypt. It’s two artificial inlets, Boughaz 1 in the West and Boughaz 2 in the East, provide a connection to the Mediterranean Sea. They enable the water bodies to interact and support fish migration. Currently, regular maintenance dredging works are necessary to keep the two inlets open.
The objective of this thesis is to analyse the effect of interventions applied to the two inlets on the lagoon-sea interaction, with the goal of transforming the present, unstable inlet system towards a stable tidal inlet lagoon by adapting one or both of the present inlets. This study is conducted on three system phases, being Phase 0, Phase 1 and Phase 2. Phase 0 consists of the initial situation without any interventions; Phase 1 contains the effect of adaptations to the Boughaz 1 inlet, and Phase 2 includes adaptations to Boughaz 2 in addition to the changes made in Phase 1. The new design in Phase 1 and Phase 2 consists of a deeper inlet cross-sectional area, the dredging of an approach channel, the addition of a nourishment, and the removal of the present breakwaters. Design elements are processed using a 2D-H Delft3D Flexible Mesh model and analysed under tide-only conditions with and without a prevailing wind climate added. Evaporation effects are included after the model calculations are made. The results are mainly assessed are the interaction with the Mediterranean Sea, the sediment transport character, and the inlet stability according to the Escoffier curve. Moreover, an analysis is made on the flushing of the lagoon and the effect of a prevailing wind pattern on the system. It is clear from both literature and the initial model results of Phase 0 that Bardawil Lagoon currently does not function as a morphologically stable tidal inlet system, as sedimentation occurs in both inlets. The water exchange between the Mediterranean Sea and Bardawil Lagoon is restricted by the inlets, which is indicated by the difference in tidal elevation on both sides of the inlet. Both inlets are positioned near the unstable equilibrium point on the Escoffier curve, indicating possible closure of the inlets in the future. Hence, interventions are required to establish a morphologically stable lagoon inlet system. By applying the proposed designs in Phase 1 and Phase 2, the limitations on the incoming tide shift from the inlets to the inner basin induces friction, thus removing the inlets as limiting factor. Moreover, taking into account both the prevailing winds and high evaporation effects, the total system is classified as having a sediment exporting character after Phase 2. High evaporation rates have a significant importing effect on the sediment transport character of the inlets. However, after Phase 2, these effects are reduced by a factor 3-5 compared to Phase 0, depending on the wind. The new cross-sectional area design also results in both inlets being positioned near the stable equilibrium point on the Escoffier curve after Phase 2, which is supported by the sensitivity analysis. Hence, it is concluded that the proposed adaptations achieve the goal of developing Bardawil Lagoon into a morphologically stable inlet system. The study provides good insight into the effect of system interventions on the morphodynamic stability of the inlets as well as the flow dominance regarding those inlets. It is recommended to construct a validated morphological 3D model which can provide insight in the long term response of the system to those adaptations.